CLASS 6TH | PHYSICS | MATTER | REVISION NOTES
Anything which occupies space and has mass is called “Matter”.
Eg. Oxygen, air, silver, steel
Characteristics of matter:
Things around us are composed of different kinds of materials. In the same material same
type of molecules are found such as in case of ice, water molecules are present.
(1)Matter occupies the space:
The volume is the amount of space occupied by the material.
(2) Matter has mass:
Any kind of material visible and invisible, has certain amount of matter in it called as “mass”
Structure and composition of matter:
Matter is made up of very very small particles in it.
These particles which make up the matter are atoms, ions and molecules
.
• Atoms :
Atoms consist of nucleus which is positive charge at centre and electrons which possesses
negative charge as in cloud around it.
In case of sodium and helium they presence in combine form as lack of individual existence
to form molecules.
• Molecules:
These are the smallest distinct units into which a pure matter can be divided. They represent
the chemical and composition property of matter.
Combination of two or more atoms result in formation of molecule. Combine atoms may be
of one kind or different. Water is made up of hydrogen and oxygen where hydrogen molecule
is made up of two hydrogen atoms.
• Ions:
Ions may be positive or negative with respect to atoms or group of atoms. Atom or group of
atom transformed to form ions when they lose or gain the one or more electron.
Eg. Sodium ion (Na+
) , Chlorine ion (Cl-
)
States of matter:
On the basis of physical property namely temperature the matter is classified into
(A)Solid -ice
(B)Liquid- water
(C)Gas- air
By changing the temperature one can easily change the states of matter.
The characteristic of matter is depend upon the arrangement of atoms or molecules inside
the matter.
The molecules of matter are held together by force of attraction between them, called as
intermolecular force of attraction. And the space between molecules are called as
intermolecular space.
These arrangement of particles inside the matter decides whether is exist as solid , liquid or
gas.
Solid states:
Characteristic by structural rigidity and with definite shape and volume. Molecules are tightly
packed due to strong intermolecular force in between solid particles .
Properties of solid :
- Have tightly packed particle
- Possess fixed shape and fixed volume
- Solid do not show fluidity
- Cannot be compressed much
Liquid state:
Characterised by the change in its shape but resistivity towards change in its volume.
They are less tightly packed as compared to solid. Within the liquid molecules are moving one
position to another, indicating fluidity.
Properties of liquid: - Have loosely packed particles.
- Have fixed volume but do not have fixed shape , take the shape of container in which
they are place - Liquid flow easily.
- Liquid cannot be compressed much
Gaseous state:
State of matter which characteristic by its capacity to change its shape and size.
They are very loosely packed as compare with solid and liquid arrangement of molecules.
They do possess weak intermolecular forces which result in molecules are far apart.
They are free to move.
Properties of gases:
- Particle within the gas , are loosely packed.
- They take the whole shape and volume of the container in which they are kept as
result of neither of fixed volume nor a fixed shape. - Gases easily flow.
- Gases can be compressed with ease into small volumes.
Effect of arrangement on the basis of their property:
The property shown by matter is depend upon the arrangement present in it.
o SOLID:
In solid structure the molecules are closely packed, in such way that their position is almost
fixed. Hence retained shape and volume. The intermolecular space is very small as the result
of greater intermolecular force of attraction between solid particles.
Application of heat onto solid, brings the extra energy to molecules and they begin to move
apart from their position finally resulting in the state change from solid to liquid.
o LIQUID:
Intermolecular space in the liquid particle is more comparable to solid as result of which due
to the weaker intermolecular force. That’s why the molecules are free to move.
Hence liquid does not possess definite shape and it takes the shape of container.
On heating liquid changes into vapour which is gaseous state. This is because on heating liquid
molecules get or acquires energy and start moving with higher speed and near the surface or
boundary get escape from the liquid and produce vapour.
o GASES:
Characteristic by fast moving particle with average speed of 1600km/hr.
The intermolecular space is wide because of very weak intermolecular force of attraction
between gas molecules.
The molecular force of attraction is depend upon the density but due to low density the force
is non-existence. Hence gas neither has shape nor have fixed volume.
On cooling the density goes on increase result into establishment of intermolecular force
which brings molecule closer and gas get converted into liquid
CLASS 6TH | PHYSICS | SIMPLE MACHINES | REVISION NOTES
Do you know you use a lot of machines every day without even knowing about it? Remember those scissors that you used to cut paper for your art class? And the stapler that you used to staple extra sheets together? They are all simple machines.
Every day you use machines without even thinking about it. A machine is anything that helps make work easier. Basic tools like staplers, screwdrivers and scissors are simple machines. These machines are all based on simple inventions like levers, planes, pulleys or wheels.
Why do we need machines?
With the help of machines, a small force can be used to overcome a large force. For example, a screw jack is used to lift an object as heavy as a car to change its tyres.
We need machines to:
- Lift heavy loads with a small effort.
- Carry out unsafe and dangerous tasks.
- To increase the speed of a moving object.
- To move, lift or perform an action in the required direction.
- To reduce the risk in performing hazardous tasks.
Simple Machines
Simple Machine:
A machine is a device that helps us to do work with less effort in less time. A simple machine has few or no moving parts.
Simple machines are basically classified into two groups, levers and inclined planes.
- Simple machines like the pulley, screw, wheel and axle and wedge come under these two categories.
- The see-saw in the playground is a simple machine.
You can use these simple machines to build a complex machine. For example, a bicycle is a complex machine that is made using of nearly every kind of simple machine.
Pulley
A pulley is a flat circular disc having a groove in its edge and capable of rotating around a fixed point passing through its central axis, called an axle.
The two commonly used types of pulleys are single fixed pulley system and the single movable pulley system.
Single Fixed Pulley System:
- A single fixed pulley system or a simple pulley consists of a grooved wheel, made of wood or metal, with a rope passing through it.
- The pulley rotates about an axle passing through its centre.
- The axle is fixed to a frame or a block.
- The pulley is normally fixed to a support above the load.
- The load is tied to one end of the rope and the effort is applied at the other end.
- Such a pulley makes our work easier by simply changing the direction of the force, i.e. a load is lifted up using a downward effort. It is easier to lift a load up by pulling it down rather than by pulling it up directly.
- Note that a simple pulley does not reduce the effort required to lift a load.
- A simple pulley is used to hoist a flag, to draw water from a well, etc.
Single Movable Pulley System
- This pulley system has a block of two pulleys.
- In this system, a load of W kgf can be lifted with an effort of W/2 kgf only.
- In a block and tackle arrangement, the pulleys are assembled together to form blocks and then blocks are paired so that one is fixed and the other moves with the load.
- The rope is threaded, or reeved, through the pulleys to provide a mechanical advantage that amplifies the effort applied to the rope.
An example of a practical application of pulleys and levers working together is the crane which is used to lift heavy loads.
The Wheel and Axle
Wheel and axle essentially consist of two cylinders of different radii joined together, such that if one is made to rotate the other also rotates. The cylinder with the larger radius is called the wheel and that with a smaller radius is called the axle.
Examples of wheel and axle system are a doorknob, a knob of water tap, a screwdriver, egg beater, a hand drill, etc.
Inclined Plane
An inclined plane is any sloping flat surface along which a load can be pushed or pulled with less effort. A hospital ramp on which a wheelchair can be pushed easily, a wooden plank used to load heavy boxes into the rear of a truck, winding roads around a hill, winding staircases, etc. are all inclined planes.
Wedge
If two inclined planes are put together to form a sharp edge, it is called a wedge. So a wedge is a double inclined plane. It works on the principle of inclined planes.
A wedge is used to tear apart or cut through objects. Knives, needles, axes, chisel, etc. are examples of a wedge.
Screw
A screw is a rod or nail with grooves on its circular curved surface and is used to hold two objects firmly together.
In simple terms, a rotating (winding) inclined plane is called a screw. The winding edge of a screw is called a thread. The grooved part of the screw is an inclined plane.
The head of the screw has a groove for the tip of a screwdriver. When the screw is held against a wooden block and its head is turned using a screwdriver, the tip of the screw moves into the wood. Because of the grooves, a screw holds the wood more firmly than a nail. Also, less force is required to insert a screw into wood than a nail because of the inclined edge.
Uses of Screws
- Screws are used to join two pieces of wood or metal. As the screw is a winding inclined plane, it cannot be pulled out easily from the attached pieces.
- A nut and bolt arrangement has two winding inclined planes. One inclined plane is on the external side of a metal cylinder and is called the bolt. The other inclined plane is on the inner side of a hollow metal cylinder and is called the nut. When the nut is given a circular motion over the bolt, it moves up or down without slipping and can withstand a lot of load.
- A cork screw is used for pulling out the cork from the bottles of ketchup or wine.
- The screw jack used to lift automobiles for repairs works on the principle of a screw.
Maintenance and Care of Machines
The following points should be remembered about the maintenance of machines.
- Machines should be protected from dust to prevent their wear and tear. So when not in use, machines should be kept covered.
- To avoid rusting due to exposure to moisture, the non-movable iron parts of a machine should be painted.
- To reduce friction, the moving parts of a machine should be regularly lubricated.
Example
Why do we have three types of levers?
A rigid bar resting on a pivot that is used to move a heavy or firmly fixed load with one end when pressure is applied to the other is called a lever. For example, imagine the incline in your parking lot that will take to your parking space in the garage.
Depending on the location of the load, the fulcrum, and the force levers are classified into three classes. They are:
- First class lever: It has a fulcrum between the force and the load, like a crowbar.
- Second class lever: It has a load between the fulcrum and the force, like a wheelbarrow.
- Third class lever: This lever has the force between the fulcrum and the load, like the arm on a human.
CLASS 6TH | PHYSICS | MAGNETISM | REVISION NOTES
Have you ever wondered why refrigerator magnets stick to the refrigerator door easily?
Magnets stick to the refrigerator door because, beneath the paint, the door is made of steel. A magnet is attracted to steel and hence sticks to the door.
A long time ago ancient people knew about the rocks that attracted metals. They were called lodestones.
The Greeks were the first to discover the phenomenon of magnetism about 4000 thousand years ago. A Greek shepherd named Magnes discovered a natural magnetic rock. This rock which had a compound of iron called magnetite was able to attract metals.
Ancient Chinese and Indians also knew about magnets.
In this chapter, you will learn about magnets, types and features of a magnet You will also learn about the properties and uses of magnets.
Magnetic Materials
Magnetic materials are those that are attracted by a magnet.
Examples: Steel, iron etc.
Non-Magnetic Materials
Non-magnetic materials are those that are not attracted by magnets. Do you know why the coins that we use are not attracted by a magnet? That s because, various metals are mixed together to make coins that are non-magnetic.
Examples: Paper, leather etc.
Magnetic Poles
Magnetic poles are the tips of a magnet and contain the highest magnetic strength. When a magnet is freely suspended, the tips point towards the north and south.
The tip pointing towards the geographical south is known as its south pole. The tip pointing towards the geographical north is known as the north pole.
Types of Magnets
Magnets are of the following two types, natural magnets and artificial magnets.
- A natural magnet is a naturally occurring substance with magnetic properties. Example: Magnetite.
- An artificial magnet is a substance into which magnetic properties are artificially induced.
- Examples: Magnets made of iron, cobalt, nickel etc.
- Artificial magnets can come in various shapes such as a dumb-bell shaped magnet, bar magnet, U-shaped magnet, cylindrical magnet, magnetic needle, etc.
- Artificial magnets are beneficial compared to natural magnets as they can be made in any desired shape.
- In addition to this, artificial magnets can be made very powerful that is not possible with natural magnets.
- Magnets made of an alloy that consists of aluminium, nickel, and cobalt (ALNICO) added to iron are the strongest magnets.
Magnets also classified as temporary or permanent based on their capacity to retain magnetism.
- Temporary magnets are those magnets which cannot retain their magnetism for a long time.
- Examples: Pure iron (Soft iron) and electromagnets that are made by passing an electric current through an iron piece.
- Permanent magnets are those magnets which retain their magnetism long after removal of the magnetising force.
- Example: Magnets made from steel (carbon + pureiron).
Uses of a magnet:
Magnets can be made into different size, shape and strength, based on their use. Devices such as TVs, loudspeakers, radios, telephones etc. make use of magnets.
Properties of Magnets
- A magnet attracts other magnetic material towards itself.
- Like poles repel each other. and unlike poles attract each other.
- A freely suspended bar magnet always aligns in the north-south direction.
- When a bar magnet is rubbed on an iron bar, the iron bar is converted into a magnet.
- There is no magnet with a single pole. Even when a magnet is cut into two pieces, each piece will behave as an independent magnet, with two poles, a north pole and a south pole.
Compass
Have you seen a compass? There must be one in the physics lab of your school. Most smartphones also have a compass. Ask your parent or neighbour to show you how the compass works.
As the needle in a traditional compass always points in the direction of the north, it is easy to find other directions easily. Let us see how the compass works.
- A compass is an instrument with a thin magnetic needle supported from a pivot.
- There is a round dial on the outer edge of the compass that marks the directions of North, South, East and West.
- The needle is positioned on a dial with marked directions.
- The north pole of the magnetic needle is painted with red colour.
- The magnetic needle in the compass always points towards the north-south direction.
- With the proper alignment of the dial, the directions can be found.
- An airtight box contains the entire assembly.
In the olden days, an old pointing device namely the south-pointing fish was used to find the directions. In this instrument, the fish head was pointed towards the south.
Storage of Magnets
A magnet gets demagnetised when left by itself for a long period of time. In other words, the magnet loses its magnetic property. This can be avoided by storing them between soft iron pieces also known as keepers when a magnet is not used. The Arrangement of bar magnets in pairs such that the opposite poles face each other and keeping two soft iron pieces at the two tips of the pair of magnets avoids demagnetisation of bar magnets.
How to Protect Magnets from Losing Their Magnetic Properties
Do not:
- Drop magnets from a height.
- Heat a magnet.
- Hammer a magnet.
Keep certain items such as DVD’s, debit cards, CD’s, audio and video cassettes, credit cards or ATM cards, and mobile phones which contain magnetic material, away from magnets to prevent damage.
Uses of Magnets
Magnets are used in:
- In stickers, magnetic toys, refrigerator doors, etc.
- Making magnetic compasses that help sailors and navigators to know directions.
- For separating iron from ores containing other non-magnetic substances.
- Removing tiny iron pieces that have accidentally fallen into the patient’s eye by eye doctors.
Electromagnets are used in:
- Generators, motors, loudspeakers, telephones, TV sets, fans, mixers, electric bells, etc.
- Cranes to lift heavy iron bars and to separate iron objects from scrap.










